Certain wireless communications systems, such as the Wireless Access in Vehicular Environments (WAVE) system defined by IEEE 1609 family of standards, are comprised of mobile vehicular units and roadside radio access units allowing connectivity into a network infrastructure. The units of these systems exchange both high priority/low latency data (e.g., emergency warnings), and low priority/best effort data (e.g., map updates). They employ a series of radio channels in the 5 GHz band, although operation in other frequency bands is also possible.
Applications, running within a vehicle or mobile host, access applications or services running on network hosts coupled to the wireline network. This is accomplished via a wireless link from the mobile host through a roadside radio connection or access device, and associated network links from the radio connection device through the network to the network host. Mobile hosts may connect through multiple radio connection devices in sequence, experiencing interruptions in connectivity while in between wireless coverage areas.
The mobile environment offers unique challenges for applications, including the following.                With relatively short range communications (e.g., 1000 m), the mobile host's communication zone is limited and its communication opportunities can be short lived.        For mobile applications, the time duration of the connection is critical. Thus, the sooner the mobile application can establish/reestablish its session after reaching an area of coverage, the longer the application has to exchange useful data.        Link quality is also paramount. It may be advantageous for a mobile device to abandon connectivity with a roadside device in order to connect to another device through a higher quality link.        In addition to link quality, it may be advantageous for a mobile device to consider the range of services being offered by a roadside device when deciding where to make its connection.        Once a connection session to the first roadside device is established, a mobile device is communicating to the first roadside device for the duration of the connection session. During that time, mobile application cannot establish a simultaneous communication session with another roadside device.        While the mobile device is communicating to one roadside device, it can still collect link quality characteristics of other nearby roadside devices.        The mobile application has to terminate the first connection session in order to establish the connection session to the second device.        
In conventional implementations, decisions are made on the basis of, first, whether a connection point is available, and second, whether it offers a service of interest to the mobile unit. Upon making connection, the connection is held as long as possible, for example, until the mobile unit moves out of range.
This results in at least two problems. The first problem is that connections might be attempted before adequate link quality is achieved, resulting in marginal or intermittent connectivity. The second problem is that once a connection is made, no attempt is made to recognize a more advantageous connection point that might become available.
Therefore, there is a need for a system and method that allows the mobile device to choose an optimal connection point when multiple connection points are available. There is also a need to mitigate the problem of attempting marginal connections.
While sharing some characteristics with cellular communication systems, the WAVE is distinct in several ways. First, a cellular system is intended to provide wide area coverage. The WAVE system uses short range communication links and often provides discontinuous “hot spot” coverage in local areas. Second, each cellular base offers a homogenous set of services (voice, short messaging, etc.); selection of the connection point is not made based on service offering. A WAVE connection point may offer a single specialized service (e.g., parking services) or a selection of services. Whereas a cellular system is engineered to minimize the overlap between adjacent coverage areas, multiple WAVE connection point, each offering its own set of services, may be located in close proximity. An example would be two parking services, each operated by a garage on each side of the street.
A cellular handset prefers to always remain in connection with the cellular network. A mobile WAVE device would prefer to be in an unconnected state where it can scan for potentially interesting services, rather than remain connected to a connection point that does not offer information of value.
These differences call for a different set of service selection methods for WAVE than have been used in cellular systems. When choosing among multiple possible cellular connections (between a handset and one of multiple base stations), the selection criteria are link quality and base station loading. Type of service is not a criterion, since base stations within a carrier's network generally offer similar services. When choosing among multiple possible WAVE connections, the selection criteria used by the invention disclosed herein are, first, services offered, and then link quality. A connection point with an uninteresting service will not be accessed, regardless of a good link quality. Likewise a connection point with a poorer link quality but more interesting set of services would be chosen over a connection point with better link quality but less interesting services.